1. Unit Ten: The Nervous System: B. Special Senses
Chapter 51: The Eye: III. Central
Neurophysiology of Vision
Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Visual Pathways
Visual Pathways
New System- the optic tracts synapse in the
thalamus and then pass to the visual cortex
Old System- the optic tracts synapse in the
hypothalamus, then into the midbrain, superior
colliculus, and then the thalamus
In humans the new system is responsible for
perception of virtually all aspects of visual form,
colors, and other conscious vision

3. Visual Pathways (cont.)
Function of the Dorsal Lateral Geniculate Nucleus of the Thalamus
Relays visual information from the optic tract to the visual cortex
Controls how much of the signal is allowed to pass to the cortex

4. Organization and Function of the Visual Cortex
Fig Visual cortex in the calcarine fissure
of the occipital cortex
Fig Transmission of visual signals from the
primary visual areas into the secondary
visual areas

5. Organization and Function of the Visual Cortex
Primary Visual Cortex- 6 major layers
Secondary Visual Cortex
Fig. 51.4

6. Organization and Function of the Visual Cortex
Color “Blobs”- receive lateral signals from adjacent
visual columns and are activated specifically by
color signals; primary areas for deciphering
color
Interaction of Visual Signals from the Two
Separate Eyes

7. Organization and Function of the Visual Cortex
Two Major Pathways for the Analysis of Visual
Information
Analysis of three dimensional position, gross
form, and motion of objects
b. Analysis of visual detail and color

8. Neuronal Patterns of Stimulation During Analysis of the Visual Image
Analysis of Contrasts
Areas if maximum excitation occur along the
sharp borders of the visual pattern
The visual signal in the primary visual cortex
is concerned mainly with contrasts in the visual
scene
Intensity of stimulation is proportional to the
gradient of contrast

9. Neuronal Patterns of Stimulation During Analysis of the Visual Image
“Simple Cells”-Orientation of Lines and Borders
Visual cortex not only detects the existence of lines
and borders but also the direction of orientation of
each line or border
For each orientation of a line specific neuronal cells
are stimulated
Cells are referred to as Simple Cells and are in
layer IV of the primary visual cortex

10. Neuronal Patterns of Stimulation During Analysis of the Visual Image
“Complex Cells”-Orientation When Displaced
Laterally or Vertically
As the visual signal progresses away from level IV,
complex cell neurons respond to orientation in
the same direction but are not position specific

11. Neuronal Patterns of Stimulation During Analysis of the Visual Image
Detection of Lines of Specific Lengths, Angles,
and Other Shapes
Detection of Color- detected by color contrast;
contrasting colors (opponent colors) excite
specific neuronal cells

12. Eye Movements and Their Control
Muscular Control of Eye Movements
Fig Extraocular muscles of the eye and their innervation

13. Eye Movements and Their Control
Neural Pathways for Control of Eye Movements
Fig Extraocular muscles of the eye and their innervation

14. Eye Movements and Their Control
Fixation Movements of the Eye
Voluntary fixation
Involuntary fixation
Saccadic movement (successive fixation)
Fixation on moving objects (pursuit movement

15. Eye Movements and Their Control
Fixation Movements of the Eye
Fig Movement of a spot of light on the fovea

16. Eye Movements and Their Control
Fusion of the Visual Image from the Two Eyes
The visual images in the two eyes normally
fuse with each other on “corresponding points”
of the two retinas
If not precisely fused, they are not in register
The nearer the object, the less the degree of register
which allows stereopsis (mechanism for judging
distances of visual objects 200 feet away
d. Is the phenomenon of depth perception

17. Autonomic Control of Accommodation
Autonomic Nerves to the Eyes
Fig Autonomic innervation of the eye

18. Autonomic Control of Accommodation
Control of Accommodation (Focusing the Eyes)-
ability to focus on near and far objects
Control of Pupillary Diameter- parasympathetic
nerves decrease the pupillary aperture and
sympathetic nerves increase the aperture